Posted
by
timothyon Thursday June 09, 2011 @01:38PM
from the so-we'll-sell-you-wifi-service dept.

mattrwilliams writes "There is a growing body of anecdotal evidence that points to personal electronics being a real issue on board planes. Dave Carson of Boeing, the co-chair of a federal advisory committee that investigated the problem of electronic interference from portable devices, says that PEDs radiate signals that can hit and disrupt highly sensitive electronic sensors hidden in the plane's passenger area, including those for an instrument landing system used in bad weather."

Well, then it seems to me the airlines should be doing something to fix it besides just trying to ban electronic equipment. If a plane can truly be put into peril with a small battery-powered transmitter then it's not going to take long for the Bad Guys(TM) to figure out how to use that as a weapon.

I hope this is not going to be another unlocked cockpit door problem where hijackings could have been easily prevented by putting a strong lock on the cockpit doors.

This is what I don't understand. With all the discussions over this, how has this not been fully tested and answered? How can we not have a definitive answer by now? And if it has been answered, why it is still being debated?

This is what I don't understand. With all the discussions over this, how has this not been fully tested and answered? How can we not have a definitive answer by now? And if it has been answered, why it is still being debated?

Because.. testing every possible consumer electronics device which might end up on an aircraft, against all the possible aircraft, and all of the possible variations of an aircraft is damned near impossible.

Some aircraft have been in production for a long time (I think over 40 years for the 747). It's got a whole boatload of variations, and has been tweaked, updated, and re-arranged by different carriers over the years. It's got different generations of avionics, in-flight systems, entertainment systems... and who knows what else. I've seen the inside of a 747 when it was stripped down to an empty shell... it's got literally miles of wiring.

Now, think about all of the different models of aircraft in the world. You would need to test 'em all.

I get the impression to be able to definitively say that no aircraft could ever be affected by this, you'd need to do testing of every possible emission from the device to coincide with every possible state of the aircraft... and some of those interferences might be intermittent or not 100% repeatable, or might be compounded by other factors they can't anticipate.

I don't think anybody has the resources to rule it out... so they've erred on the side of safety. The sheer cost of trying to test this extensively would be enormous.

And, really, unlike the pharma industry which waits until you can prove that something is causing harm before they pull it, the airline industry is waiting for proof that it doesn't cause harm before they allow it.

So, why can't they show it/test it for at least ONE plane. Heck, put all the currently shipping PED's on the plane and get actual proof one way or another. Or fill a plane with people, giving every person the highest radiative device currently shipping, and see if there's any interference. They don't have to do EVERY plane. But how about start with ONE plane, at a maximum conditions for PED radiation.

But when they only have anecdotal evidence - from the head of Boeing - it just comes off as FUD.It's not

We do this test every day. On any aircraft of reasonable size, there are at least a dozen cell phones not in the off position during takeoff and landing. Probably more. Most of these jets carry a hundred or more people. Nearly 100% of people carry some sort of electronic devise. Anyone here work in IT? Care to guess how many of your normal users will follow instructions? Does anyone seriously believe they get much north of 90% compliance with the "all electronics must be in the off position" request under the best circumstances? How many rings, pings, and update sounds do you hear on final approach when you come in low enough for the cell signal to connect? I hear so many I don't even notice anymore.

If this were a truly serious problem, we'd have planes dropping out of the sky like rain. I couldn't say that there isn't a potential for a problem. I can say that the risk must be very, very small.

If this were a truly serious problem, we'd have planes dropping out of the sky like rain. I couldn't say that there isn't a potential for a problem. I can say that the risk must be very, very small.

The thing is, they're not claiming that it is a truly serious problem, or that the risk is anything other than very, very small. In fact, they highlight only 75 incidents (note: "incident" is a specific aviation term that is differentiated from "accident") that may, or may not, have been attributed to personal electronic devices.

So, while you're correct in saying that we do this test every day, it's also true that the tests don't show 100% success. There are certain cases, however rare, where these devices

If this were a truly serious problem, we'd have planes dropping out of the sky like rain.

That's like saying "seatbelts are totally unnecessary because I have been driving for 20 years without one and haven't been injured yet".

No, it's like saying, "seatbelts are unnecessary because no one has EVER demonstrably been hurt by not using them." Hundreds of millions of people fly every year, a substantial percentage of them use electronics and don't bother to turn them off (in my experience), and it's still the safest form of transportation -- without a single confirmed death due to electronic use.

I'm not saying that the ban is good or bad, only that your analogy sucked.

According to BTS statistics, there were approximately 9,500,000 revenue departures in 2009, or about 26,000 per day... in the US alone. That doesn't count private flights, which tend to TRIPLE the numbers involved.

Given that dozens of people ignore the rules or forget to turn off devices on each and every flight... the law of large numbers would say otherwise....

This is why you occasionally get stories like the FAA knocking on a guy's door because his TV is emitting noise on a distress beacon frequency.

Not the FAA. The Civil Air Patrol and the local police/sheriff.

I was there for one of these. A Toshiba TV/DVD player combo. For some reason unknown it was emitting a VERY STRONG unmodulated carrier on 121.5MHz. So strong that the SARSAT system was picking it up and it was blanketing any other potential ELT in the area.

It was an early Sunday morning. Half a dozen cops, half a dozen uniformed CAP cadets, and a couple of SAR volunteers. A hapless college student was watching Sesame Street in his underwear.

We couldn't pin it down until one of us noticed that the signal had stopped when he answered the door. We asked "did you just turn something off?" and the rest is history. His TV was two days out of warranty, but Toshiba swapped it out anyway so they could test the thing to find out why it was emitting. There was no visible sign of any problem with the TV, nothing looked wrong, everything was working. It wasn't until we showed up at his door that he found out there was a problem.

Anyone who says that personal electronic devices cannot interfere with aircraft systems is ignorant at best. Properly designed, properly maintained, properly functioning PED in a properly designed, properly maintained, properly functioning aircraft has minimal chance, but too many things break too often and the costs are very high, so why risk it? So you can text your BFF that "hey, lolz, I'm on an airplane?"

It's also possible their systems are shielded to handle EMP bursts and all sorts of other craziness that you wouldn't experience on commercial flight.Not to mention E-8 and E-3 are hauling around huge radars that pump out alot of energy. Finally, I would imagine alot of shielding is to protect the devices from said radar coming from airplane instead of protecting the plane from the devices.

That's a nice image, but it's a standard rugadized pda. You can find similar hardware for doing work in factory environments and such where you potentially need to protect the electronics from more abuse than your average consumer electronics are designed to take. It really has nothing to do with preventing interference.

Actually, that's more about meeting TEMPEST requirements so as to not emit a signal from which an enemy can derive useful information. Hardening of the avionics is a different thing, and not something one will readily find an image of.

No indication that anything in that pic is TEMPEST rated. Just looks like a lot of rubber around what may be a fat bundle of skinny little wires.

Besides which, there are no safety standards for military gear; at least, not as such. Military aircraft don't have to follow the standards that the FAA specifies for commercial aircraft (DO-178B, DO-254, etc.)

The question here is, okay, so what? They measured ERP for a few PEDs. Does that signal have any way to be coupled to the actual equipment they're worried

You talk about amateur radio, with a number of mostly AM, SSB, and CW modulated traffic, and not all at 5KW. And they don't affect your *AUDIO* system.

Now imagine air speed indicators, small aperture radar, and some highly sensitive receivers that get bombarded with harmonics from laptops, game controllers, tablet/pads, GSM/CDMA phones, and other personal devices, any or all of which might be blurting out naturals or harmonics from their screens, USB devices, and so on.

Actually, yes. How about something regarding consequences? Say 100+ people in a fragile machine, surround by flammable liquids, moving at a high rate of speed and doing so with limited to no visibility outside the machine having a "mishap" because someone had to check twitter? There are some activities where an excess of caution is warranted, personally I believe that needing to use an ***instrument landing system because of bad weather*** is one such activity.

Actually, yes. How about something regarding consequences? Say 100+ people in a fragile machine, surround by flammable liquids, moving at a high rate of speed and doing so with limited to no visibility outside the machine having a "mishap" because someone had to check twitter? There are some activities where an excess of caution is warranted, personally I believe that needing to use an ***instrument landing system because of bad weather*** is one such activity.

Actually I'm saying that flying planes is dangerous, and that given that *many* lives are at risk the burden of proof should be that a device needs to be proven safe, not that it needs to be proven hazardous.

There is a growing body of anecdotal evidence

Need I say more?

Actually, yes. How about something regarding consequences? Say 100+ people in a fragile machine, surround by flammable liquids, moving at a high rate of speed and doing so with limited to no visibility outside the machine having a "mishap" because someone had to check twitter? There are some activities where an excess of caution is warranted, personally I believe that needing to use an ***instrument landing system because of bad weather*** is one such activity.

the burden of proof should be that a device needs to be proven safe, not that it needs to be proven hazardous.

Perhaps you should stop making up panicky, ridiculous statements like "the machine having a "mishap" because someone had to check twitter" and come up with something more sensible and, as the GP noted, based on empirical evidence instead of anecdotal evidence.

If personal electronics carried by a passenger are a threat to avionics, then the problem is in how the plane is constructed. Otherwise they'l

the burden of proof should be that a device needs to be proven safe, not that it needs to be proven hazardous.

Perhaps you should stop making up panicky, ridiculous statements like "the machine having a "mishap" because someone had to check twitter" and come up with something more sensible and, as the GP noted, based on empirical evidence instead of anecdotal evidence.

Your statement seems to dodge the issue that many lives are at risk and that this should shift the burden of proof. In other areas where lives are on the line the burden of prove is to prove safety, why not here? Why not require the scientific evidence to demonstrate that the device are safe?

If personal electronics carried by a passenger are a threat to avionics, then the problem is in how the plane is constructed.

Even if true, and given that the planes and avionics were designed before the devices in question existed this may be the case, however what is the remedy? Ban the airplane/avionics or ban the device during landing?

It doesn't really matter if the problem is the way the plane is constructed or the devices themselves. The fact is, there can be interference (yes, I do trust an Associate Technical Fellow at Boeing more than random slashdotters). So now the question is: what to do about it?

Option 1 is to refit all the planes currently in use so they are not susceptible to interference. Since the airlines are already teetering on the edge of bankruptcy, and the flying public has shown no taste at all for increased fares

Picture one person on the plane with a device designed to interfere with the avionics. The device looks like a cell phone, but when turned "off", it really goes into "interfere mode". This is why I see it as idiotic that the avionics aren't hardened well enough to deal with unintentional interference from devices designed to minimize interference...

Actually, yes. How about something regarding consequences? Say 100+ people in a fragile machine, surround by flammable liquids, moving at a high rate of speed and doing so with limited to no visibility outside the machine having a "mishap" because someone had to check twitter? There are some activities where an excess of caution is warranted, personally I believe that needing to use an ***instrument landing system because of bad weather*** is one such activity.

Here's the problem with this reasoning. Much work has been done to prove a connection using scientific methods. The answer? Nope - not a problem - but let's keep looking, because, as you said, this is dangerous and important. And you say "Screw the science - anecdotal is good enough - cause it is dangerous!" Well, I'm sorry, but just because a friend of mine swears that genetically altered food contains arsenic because he got sick once, and was told he had food poisoning after eating an apple, doesn't

Actually, yes. How about something regarding consequences? Say 100+ people in a fragile machine, surround by flammable liquids, moving at a high rate of speed and doing so with limited to no visibility outside the machine having a "mishap" because someone had to check twitter? There are some activities where an excess of caution is warranted, personally I believe that needing to use an ***instrument landing system because of bad weather*** is one such activity.

Here's the problem with this reasoning. Much work has been done to prove a connection using scientific methods. The answer? Nope - not a problem - but let's keep looking, because, as you said, this is dangerous and important. And you say "Screw the science - anecdotal is good enough - cause it is dangerous!" Well, I'm sorry, but just because a friend of mine swears that genetically altered food contains arsenic because he got sick once, and was told he had food poisoning after eating an apple, doesn't mean it's something to freak out about - even though food poisoning is dangerous, and yes, it's possible he could have died.

The pitot tubes on certain Airbus aircraft were heavily tested using scientific methods and found to be safe. Reports of problems were probably considered anecdotal by some. Yet we eventually had a catastrophic loss of life where we found that the scientific methods employed failed to uncover a design flaw.

Your analogy is also severely flawed. Eating is a necessity. Using a handheld device during landing is not.

Is there some good reason we shouldn't test against this? It's possible the people who originally did the tests didn't create the circumstances these anecdotes suggest. I'd rather be safe than sorry, but that's just me and my flying preference.

Asked if a cellphone's signal could really be that powerful, Carson said, "It is when it goes in the right place at the right time."

To prove his point, Carson took ABC News inside Boeing's electronic test chamber in Seattle, where engineers demonstrated the hidden signals from several electronic devices that were well over what Boeing considers the acceptable limit for aircraft equipment. A Blackberry and an iPhone were both over the limit, but the worst offender was an iPad. There are still doubters, including ABC News's own aviation expert, John Nance.

"There is a lot of anecdotal evidence out there, but it's not evidence at all," said Nance, a former Air Force and commercial pilot. "It's pilots, like myself, who thought they saw something but they couldn't pin it to anything in particular. And those stories are not rampant enough, considering 32,000 flights a day over the U.S., to be convincing."

That's not how burden of proof works. I could say that wearing a hat slightly to the left causes the plane to rapidly descend and then qualify it by saying I heard it from a bloke in the pub who knows for definite and that has a much evidence as this article suggests. If I thought it was true then I would have to supply evidence to support it other than the bloke in the pub who knew for sure. The burden of proof rests with the person making the claim.

Are you saying we should err on the side of convenience or err on the side of safety? Or are you saying that the extrodinary claim that no consumer electronics cause interference with commercial avionic systems requires extrodinary evidence of that claim?

On the other hand if they can show one counter example of an electronic system causing interference, then it's a low burden of proof, right? Well someone tried this (mythbusters episode 49), and it turned out to be plausable, so the burden of proof shif

Not to mention that if an effect is real and measurable, it will have anecdotal evidence.

I think it's pretty indisputable that electronic devices can cause interference in other devices be they tvs, radios, or airplanes. Is a cell phone going to bring down a plane? I seriously doubt it, but i'd like to think that aviation as a rule is a risk averse field. Why use up resources chasing after these ghosts when the simple solution is just turn your cell phones off?

What the airlines should probably do is offer reward miles to people who turn their phones off promptly on the plane.

If planes switched to fiber optics and got rid of copper wiring I'm sure that would reduce the likelihood of interference. I can hardly wait for the day people will be able to use their cell phones on those long haul flights.

I can hardly wait for the day people will be able to use their cell phones on those long haul flights.

As a daily train commuter, whose most hated sound is someone shouting "NO, I'VE GOT PLENTY OF TIME, I'M ON THE TRAIN!" into their cellphone, I can only warn you to be really, really careful what you wish for.

Of course you were being facetious, but aircraft paint is heavy and must be taken into account in weight-and-balance calculations to ensure the aircraft is stable and not overweight after painting.If too much paint accumulates, it must be removed and the paint cycle begun again.

What's your point? Those are two entirely different things.
Some appliances can handle a firehose spraying directly at them, but break when subjected to water vapor.. Just as related, actually, no even more related.

I was too! I had to look it up immediately after the pilot informed us all that we need to turn off our cell phones. I just didn't believe that someone with years of experience and training could be smarter than the internets.

Any story that gets the details that wrong, that fast, receives no credence at all. And if airplanes are having this much trouble with my 2mw iPad, what the *hell* are they doing about getting hit by 2GW of lightning?

(And don't tell me "Faraday cage"; that protects the occupants, but not necessarily the things connected to antennas outside the cage.)

Assuming the sensor isn't destroyed by the lightning, the EM radiation from a lightning strike that would cause interference is short-lived. It probably does cause interference with a number of sensors, but only for a short time. If a personal electronic device is causing interference, that interference is likely to persist for the entire flight.

As i was told in mid 90 by my electromagnetism teacher, the problem is not the miriad of (then) walkmans and cd player used in the plane. Those are more or less certified for electromagnetic compatibility. The problem are the crappy chinese electronics that don't pass any test and the one in a million "certified" hardware that is faulty. So, do you prefer listen your music and risk your life in an emergency situation or forbid them all just in case?

Reminds me of when I took my electromagnetics class. The professor had brought his daughter's tickle me Elmo doll into class. I don't remember what device it was that he had, possibly it was his car's remote key entry system remote, but when he click one of the buttons, he was able to make the tickle me Elmo doll activate and start laughing. This would probably be one of you million to one examples, but I think the crux is the same. If someone doesn't design properly, or well for EMI, then stuff like this c

Studies cost money. Everything costs money. With a finite amount of money, you prioritize. And this isn't a big enough problem to warrant spending money studing. So instead of paying a bunch of test engineers to undertake a bunch of tests (which to be useful would have to be re-run on practically every aircraft configuration), you hire one guy to look at the anectdotal evidence. Best case, your studies would prevent a couple of crashes over the span of a human lifetime, saving a few hundred lives. Muc

Studies cost money. Everything costs money. With a finite amount of money, you prioritize. And this isn't a big enough problem to warrant spending money studing.

Seriously? The number that a casual Google search shows is about 28,000 commercial flights a day. Multiply that by a conservative 75 people a flight and you get at least 2,100,000 people taking a flight per day, just in the US . You think that doesn't warrant an all-out investigation to resolve the questions involved in a methodical and scientific manner, regardless of the cost?

Perhaps the airlines are more interested in monetizing the use of said devices and the studies would possibly show something di

We don't know whether the presence of ragweed near an airport causes a significant increase in the rate of accidents. We also don't have any anecdotal evidence that it does. There's no basis for research - yet. But if a couple anecdotes start to circulate, it may actually point to something that deserves research.

Also, in this case, the GP has a point. It may actually make more sense to trust the anecdotal evidence than do a rigorous study, because of the cost of a rigorous study: the mild inconveniences of

I call bullshit. These instruments are TEMPEST shielded to such a degree it's ridiculous. Personal devices also don't emit with enough power (unless modified) to affect anything further than a couple of feet away from them.

I had always been suspicious of the reality of small electronics and avionics interference, but now I have some first hand experience--I fly a small airplane (a Decathlon). Granted, it has much different RF characteristics than a large airliner. Like most airplanes, it is equipped with a transponder that encodes the airplane's altitude and transmits it when the air traffic control radar paints the airplane. Sometimes when my iPhone is turned on in the airplane, the altitude reported by my transponder varies wildly by several thousands of feet, and air traffic control tells me they are getting spurious signals. One day when this was happening, I thought ah heck and I turn off the phone, and the transponder settled down. I turned it back on, and the transponder started going wonky again. I've reproduced this on a few different days and most days with no issues with the phone turned on. I'd say it's 20% bad/80% good. I haven't figured out what conditions cause this to happen or not--could be poor equipment installation. Anyone else with actual experience of something like this happening?

As an engineer who designs and integrates RF systems every day, all day, I have two impressions. And as a systems engineer, I'll describe them in terms of the two elements of risk: probability and impact.

FTFA: "In other events described in the report, a clock spun backwards and a GPS in cabin read incorrectly while two laptops were being used nearby."

First: Crap like that ain't supposed to happen. An airplane designed and built to standards for commercial passenger service must meet standards for electromagnetic susceptibility, interference tolerance, workmanship, etc. It's not the passengers' fault that things like that happen. Nor is it the direct fault of the manufacturer of the electronics that passengers carry. If something is that mission critical, and the cost of failure is measured in human lives, then engineers, inspectors, regulators, and operations crew damn well better make sure the likelihood of failure is as close to zero as can be.

Second: I know damn well that grounding and shielding is one of the most difficult aspects of any high-frequency electronics system. It's difficult to design, grounding and shielding design rules aren't generally taught as part of undergraduate EE curriculum (much less Aeromechanical, CS, etc.), and the manufacturing techniques are prone to failure and not easy to inspect and test. Therefore, statistically, a passenger that travels one or two times a year is likely to board a plane with a design flaw or manufacturing/maintenance flaw at some point in their lifetime. This doesn't mean they're going to notice it, or even have any effect on the flight, much less cause an emergency by forgetting a powered-up iPhone in their carryon. But the likelihood of failure will never be zero unless the passenger obeys the rules and turns off their devices.

So, turn your shit off when so instructed.

And consumer electronics designers: please give the consumer a switch that allows them to turn their shit off... not standby, but OFF.

Just because you are 'an engineer' who 'works with RF' doesn't mean you know tiddly about avionics. I actually work at an avionics lab and repair and test these devices and have actually measured RF interference of avionics systems, both on the ground and in the air. Its my job.

As a fellow engineer I could give you a 5 minute brief on how the ILS system works, another 15 to go through explaining all the board level receiver circuits, data busses and another 20 to go throught the navigation computer and autopilot at block diagram level - and afterwards you'd be rolling on the floor laughing to the very idea of a passenger ipod being able to interfere with 'the ILS system'... unfortunately my superiors are hunting me down to lock me back to my cave now.

Somewhere there is an engineer that argued quite vehemently that there is no way the air speed sensors on an Airbus A330 could possibly all fail

There is/was no engineer that argued this. Instead the argument was, "if this happens, what can we do to improve safety in that event?" That failure mode was thought of, I have absolutely no doubt. Engineers thought it was covered, they may have been wrong about that but I'll discuss that later.

leading the engines to stall in mid-flight

An aircraft stalling does not involve the engines, it involves airflow over the wings. Do you have any knowledge of the topic at all? Nothing I've read indicates there was an engine failure on that flight.

The aircraft crashed because when readings became invalid, the computer automatically disconnected the autopilot / autothrottle (as it should have). The pilots then made control inputs that were inappropriate for the situation. They were probably confused by the relative lack of data they had, and the multitude of warnings a complete air data failure causes. The pilots then held a nose up attitude through multiple stall warnings, eventually entering a period of extremely high sink rate. The aircraft had pitched up in excess of 35 degrees through this period, and the pilots held full nose up control inputs through almost all of it. It was the exact opposite of what they should have been doing. The pilots held the stall all the way into the ocean, impacting the water while still in a nose up attitude of more than 16 degrees.

I know people like to get up in arms whenever a crash is blamed on pilot error, but it's pretty clear in this case that the pilot's actions were inappropriate and their inability to recover from the stall despite ample opportunity will almost certainly be listed as the main cause of the accident. There were many contributing factors, but the data suggests that the aircraft would have flown just fine if given proper stall recovery inputs.

What could the engineers have done better? Indicate in a more useful way what was going on and which instruments were reliable. The pilots should have been able to tell at a glance what they should pay attention to and what they should ignore. The avionics display design may not have been good enough for them to do that. The stall warning may have deactivated inappropriately based on the invalid speed, because the computer thought the aircraft was traveling too slow for the angle of attack indicators to function correctly. This failure mode should not exist in my opinion. Either the angle of attack indicator should function at lower speeds, or an alternate stall indication should be used instead. Or just keep the warning on, since the aircraft is quite obviously not in landing configuration. From what I read, they were probably assaulted with a whole host of failure warnings that were confusing and may have contributed to a panic reaction.
Also, pilot training needs to be improved in some areas, especially involving loss of pitot static data. There is no reason an airplane of any type should crash because of a clogged pitot tube. This should be drilled into pilots starting with the most basic beginning flight training. I know from experience the topic is not covered at that level, besides a couple questions that may appear on the knowledge test. In fact, if I had not actually had a pitot tube get clogged during my training, I would have never encountered the situation at all.

There's some fairly good discussion about the events of the flight here [flightglobal.com].

To me this just means that Boeing engineers need to do a better job of shielding their sensors. The world has advanced, people have such devices and flights are getting longer. I dont want to use/pay for the crappy entertainment system on the plane. I want to use my own. I understand that this might not be the priority for them right now, but it needs to happen sometime soon.

On a recent Delta flight from Orlando to Minneapolis, I had the pleasure to sit next to a Delta employee on the same trip. He didn't even bother turning his iPhone on airplane mode.. in fact he was checking his email during takeoff and landing.

If this were actually that bad of a threat, don't you think TSA/DHS would have adjusted their policies regarding PEDs onboard? Give me a break. Chances are they're crying wolf so they can try and secure a few billion in funding to upgrade all of their aircraft wiring and shielding under the guise of "homeland security", so taxpayers can somehow pay for it instead of the "poor starving" airlines.

If there is or may be a problem, then develop a standard for both the electronic device maker and the navigation system maker can work with.
I'm sick and tired of airplane makers saying that everyone must shut down all possible electronic devices or the airplane will crash into the ocean
Does that include pace makers?
How about artificial limbs that are electrically powered?
Navigation systems should be defined to work with a given amount of noise on various frequency bands.
It is not reasonable in today's

I had always heard that the real reason they make you turn off electronic devices is so that you listen fully to any instructions you are given. Why else would they make me turn off my wi-fi only Kindle?

Maybe. I think that the "cellphone interference" is just a blanket term they use whenever anything goes wrong. When I was flying from PSP to DFW a few months ago, the flight attendants had already given the "turn off all electronic devices" thing followed by the safety brief, yet we still hadn't moved onto the runway. Instead of telling us what the hold up was, the flight attendant got on the intercom and said, "We would be on the runway right now, but somebody left their cell phone on and it's interferi

1. Personal electronics are safe, this is just BS.
2. Personal electronics are not safe, thus if a terrorist wants to crash a plane, all they need to do is use an iPad.

How about3. The safety is unknown, and is utterly impractical to determine for all combinations of airplanes and electronic gadgets.

And your point 2 is of course nonsense: even if some electronic gadget would be known to interfere with the functioning of an airplane, it wouldn't mean that switching on the gadget in the plane would make that plane unavoidably fall out of the sky.

Your false dichotomy assumes that the chance of the interference from a personal electronic device is either 0% or 100%. (Or at least, near enough to 100% to be used as an attack.)

It's obviously not 100%. I know plenty of people who have forgotten to turn off cell phones and other devices for the entire duration of the flight. That doesn't guarantee that the interference from the devices could never cause a fatal problem.

1) Many airlines let you carry 1 litre of vodka onto their plane. That's definitely more dangerous than 1 litre of water:).2) There is usually no penalty if they catch you, you're allowed to chuck the item into a bin. They assume it won't blow up the bin;).